What is the neurohypophysis?

The pituitary gland is divided into two sections: the anterior lobe and the posterior lobe. The neurohypophysis is the name given to the posterior lobe (part) of the pituitary gland. The neurohypophysis stores and releases several hormones created by the hypothalamus - a small region at the base of the brain.

The antidiuretic hormone (ADH) is a hormone that is released from this part of the gland which is responsible for controlling water reabsorption and retention. When a patient suffers from the syndrome of inappropriate antidiuretic hormone secretion (SIADH) - where the body makes too much ADH - the kidneys retain too much water causing low levels of electrolytes, such as sodium. If your body doesn’t have enough sodium, it causes uncomfortable symptoms such as muscle weakness, irritability and restlessness, loss of appetite, cramps, vomiting, seizures and coma.

What does the neurohypophysis do?

The neurohypophysis is responsible for storing and releasing two important hormones: oxytocin and vasopressin (also known as ADH). These hormones are found in most mammals that display dynamic physiological and behavioural actions. It is commonly thought that the neurohypophysis produces hormones, which is incorrect, as it only stores and releases them.

• Oxytocin: this is a hormone that’s released during social bonding and plays an important role during childbirth, causing the womb (uterus) to contract.
• Vasopressin: the main functions of this hormone are to regulate the tonicity of body fluids. It causes the kidneys to reabsorb solute-free water and return it to circulation. It also has an important role in social behaviour, sexual motivation (especially in men), blood pressure regulation and temperature regulation.

What are the possible complications?

Diseases that may affect the neurohypophysis include those secondary to the defect or excess production of the antidiuretic hormone (ADH). An injury, degeneration or impaired functioning can cause the neurohypophysis to deregulate the secretion of oxytocin and vasopressin.

• Diabetes insipidus (DI): this is a rare condition characterised by large amounts of dilute urine and increased thirst. ADH enables the kidneys to retain water, so when there is a problem in the release of this hormone, the patient can excrete up to 20 litres of diluted urine per day.
• Syndrome of inappropriate secretion of the antidiuretic hormone (SIADH): this is when the body makes too much ADH. This hormone controls how much water in your body is lost through the urine and SIADH causes your body to retain too much water. It is mainly caused by drugs and causes gastrointestinal, respiratory, neuromuscular and neurological symptoms.

Treatments

Typically, diabetes insipidus is treated with a man-made form of the vasopressin hormone called desmopressin. It can be administered orally, as a nasal spray or injected. It works by replacing the missing hormone (ADH) which, as a result, reduces excess urination.

In regards to the syndrome of inappropriate secretion of the antidiuretic hormone, treatment normally involves restricting the amount of fluid, and if possible, treating the underlying cause. Sometimes intravenous fluids are administered, including those with high sodium concentrations, however, these must be given carefully to avoid rapid increases in sodium levels. Some drugs can be given if these treatments fail, such as demeclocycline or lithium, which restrict the effect of vasopressin on the kidneys.

Which specialist treats neurohypophysis disorders?

A doctor responsible for treating diseases related to the neurohypophysis is an endocrinologist.